Wireless communications devices such as cellular telephones, two-way radios, personal digital assistance, wireless personal computers, laptop computers, home entertainment equipment, et cetera that communicate either directly or indirectly with other wireless communication devices. Each wireless communication device participating in wireless communications includes a built-in radio transceiver (i.e. receiver and transmitter). The transmitter of a wireless device typically includes a data modulation stage, one or more frequency conversion stages, and a power amplifier. The power amplifier amplifies the RF signals prior to transmission via an antenna. The power amplifier must operate at high frequency, provide a high swing at its output, be very linear in its operation, and use as little power as possible. These competing goals are very difficult to meet, particularly in portable devices that are battery powered and operate at relatively low voltages.
A typical RF power amplifier circuit (PA) is shown FIG. 1A. The PA circuit consists of two cascoded transistors: a low voltage (gain) transistor 20 with thin gate oxide and a high voltage (cascode) transistor 26 with thick gate oxide. An inductor 32 and output load matching network 30 circuit produces an amplified voltage swing 36 as shown in FIG. 1C. The peak mid voltage 36 at the cascode transistor 26 drain terminal may be approximately two times the power supply voltage 32. The matching network may be a transformer which may produce an even higher voltage, Vout-peak, 38 which may be 4*Vdd for example into load resistance 34 which may be an antenna. The gate dielectric on the cascode transistor 26 is sufficiently thick to withstand 2*Vdd without damage when the cascode transistor 26 is switched off. The turn on voltage of the high voltage transistor, Vthv, must be sufficiently high so that the maximum voltage, VLOW-peak 18, on the common diffusion 24 between the cascode transistor 26 and the gain transistor 20 in FIG. 1B does not exceed the voltage capability of the thin dielectric on the low voltage (gain) transistor 20. This voltage is equal to the voltage on the high voltage (cascode) transistor gate 26 minus the threshold voltage on the high voltage (cascode) transistor 26, Vthv. (VMID-peak<=VGC−Vthv).